A 5-year-old Cumberland County mare is the first reported case in 2017 of Eastern equine encephalitis (EEE), a serious mosquito-borne illness.

The horse had not been vaccinated against EEE and died on Aug. 28.

“Horse owners need to be vigilant in vaccinating their animals against diseases spread by mosquitoes,” said New Jersey Secretary of Agriculture Douglas H. Fisher. “Vaccinated animals are much less likely to contract deadly diseases such as EEE and West Nile virus.”

The disease is transmitted by bites from infected mosquitoes. The virus cycles between birds and mosquitoes with horses and humans being incidental dead-end hosts. Horses cannot transmit EEE to humans or vice versa.

A viral disease, EEE affects the central nervous system. Clinical signs of EEE include moderate to high fever, depression, lack of appetite, cranial nerve deficits (facial paralysis, tongue weakness, difficulty swallowing), behavioral changes (aggression, self-mutilation, or drowsiness), gait abnormalities, or severe central nervous system signs, such as head-pressing, circling, blindness, and seizures. The course of EEE can be swift, with death occurring two to three days after onset of clinical signs despite intensive care. Horses that survive might have long-lasting impairments and neurologic problems.

In 2016, New Jersey had four cases of EEE and no cases of West Nile virus (WNV).

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Effective equine vaccines for EEE and WNV are available commercially, and owners should contact their veterinarians to ensure horses’ vaccines are up-to-date. Horses that have not already been vaccinated this year for EEE or other mosquito-borne diseases are at greater risk, but it is not too late to vaccinate. Horses that have been vaccinated in past years will need an annual booster shot; in areas with a long mosquito season, veterinarians might recommend two boosters per year—one in the spring and one in the fall. However, if an owner did not vaccinate their animal in previous years, the horse will need the two-shot vaccination series within a three- to six-week period.

In addition to vaccinations, horse owners also need to reduce the mosquito populations and their possible breeding areas. Recommendations include removing stagnant water sources, keeping animals inside during the bugs’ feeding times, which are typically early in the morning and evening, and using mosquito repellents.

Both EEE and WNV, like other viral diseases affecting horses’ neurologic system, must be reported to the state veterinarian at 609/671-6400 within 48 hours of diagnosis. The New Jersey Animal Health Diagnostic Laboratory is available to assist with EEE and WNV testing and can be reached at 609/406-6999 or jerseyvetlab@ag.state.nj.us.